Hi
I’m observing an interesting behavior while evaluating GraphCast forecasts against ERA5 data.
When plotting the global mean of near-surface temperature variables, specifically t1000 and t2m, the forecast mean oscillates in sync with ERA5, which looks physically correct and expected.
However, the global mean RMSE computed for a single 40-step (6-hour interval) run also shows a noticeable oscillatory pattern instead of a smooth or gradually increasing trend.
Is this RMSE oscillation expected, or does it indicate an underlying issue with how RMSE is being computed or with the model’s short-term stability?
Details:
Model: GraphCast-Small (1.0° / 13 levels)
Forecast length: 40 steps (6-hour intervals)
RMSE computed as global cosine-latitude-weighted mean over all grid points and times
Both forecast and ERA5 data are aligned on valid time coordinates before evaluation
RMSE typically increases smoothly with lead time, so I wanted to confirm whether oscillations in RMSE are normal behavior for GraphCast for near-surface temperature variables.
Hi
I’m observing an interesting behavior while evaluating GraphCast forecasts against ERA5 data.
When plotting the global mean of near-surface temperature variables, specifically t1000 and t2m, the forecast mean oscillates in sync with ERA5, which looks physically correct and expected.
However, the global mean RMSE computed for a single 40-step (6-hour interval) run also shows a noticeable oscillatory pattern instead of a smooth or gradually increasing trend.
Is this RMSE oscillation expected, or does it indicate an underlying issue with how RMSE is being computed or with the model’s short-term stability?
Details:
Model: GraphCast-Small (1.0° / 13 levels)
Forecast length: 40 steps (6-hour intervals)
RMSE computed as global cosine-latitude-weighted mean over all grid points and times
Both forecast and ERA5 data are aligned on valid time coordinates before evaluation
RMSE typically increases smoothly with lead time, so I wanted to confirm whether oscillations in RMSE are normal behavior for GraphCast for near-surface temperature variables.